Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EST Sun Jan 08 2023 Valid 12Z Thu Jan 12 2023 - 12Z Mon Jan 16 2023 ...Overview... The consensus of latest guidance shows no meaningful change in the expected pattern evolution from late this week into early next week. An east-west upper ridge should build over the southern mainland by Friday after passage of a shortwave on Thursday, with the ridge axis becoming more southeast-northwest oriented over time. While this ridge and the longer term ridge over Canada persist through the end of the forecast, the overall ridging should trend gradually weaker. Farther north, energy from an upper low initially near the eastern tip of Siberia should shear out into an upper weakness expected to set up near the northern coast of the mainland. The strong storm tracking into the Aleutians with a period of enhanced precipitation/winds during the latter half of the week will likely linger over the area into the weekend as it slowly weakens. The flow around the mainland/Canada upper ridge and ahead of the Aleutians storm may carry one or more low-predictability waves that could support episodes of precipitation anywhere between the eastern Aleutians and Panhandle. Surface low details become increasingly uncertain late in the period, but within a broad favorable area for low pressure from the Bering Sea/Aleutians/North Pacific eastward. ...Guidance/Predictability Assessment... About the first half of the forecast emphasized the 12Z GFS/ECMWF with lesser input from the 12Z UKMET and least from the 12Z CMC. This solution provided good overall continuity for the mainland pattern, with some refinement of the eastern Siberia upper low expected to help form the longer term weakness near the northern coast of the mainland. There is still some spread for where this upper low/weakness ultimately sets up, with an average of recent GFS/ECMWF runs closest to the ensemble means but the UKMET/CMC somewhat farther north. The strong Aleutians storm also displays good continuity in principle with only modest and typical day-to-day adjustments. GFS/ECMWF runs and the UKMET all suggest that the system should be in the mid-upper 950's mb as of early Thursday and still in the lower 960's early Friday. The leading front anchored by this storm may develop an embedded compact wave that could race northward from the Pacific into the Bering Sea, but for now with seemingly random ideas for specifics in the guidance. Over the northeastern Pacific, the signal has trended more faint for a possible system that could bring some moisture to the Panhandle from the south around Friday. Today's forecast depicts a well offshore feature with a dissipating front as a transition from yesterday's more defined system. While the forecast over the mainland remains fairly agreeable and stable through the end of the period, details over the Pacific/Bering Sea become increasingly uncertain. Thus the forecast blend trended close to an even blend of ensembles (12Z GEFS/00Z ECens) and models (GFS/ECMWF) by days 7-8 Sunday-Monday, splitting input from each of the two models among their last two runs to dampen the influence of any one particular model run's low on the forecast. There is good consensus for a strong mid-latitude jet to start progressing across the Pacific during the latter half of the period, leading to a more elongated upper trough across the Aleutians/southern Bering Sea into the northeastern Pacific by the start of next week. Ensemble members and individual model runs show a broad area favorable for low pressure existence across this area, but very poor agreement for specifics. This includes a split in guidance for whether original Aleutians low pressure lingers over the Bering Sea lingers through the end of the period or is replaced by an upstream low (which itself could track as far north as the Bering Sea or miss the Aleutians well to the south). The northeastern Pacific looks fairly chaotic as well. Thus the emphasis should be on the general forecast of low pressure/unsettled weather over this broad area rather than the specifics of a manual or model forecast. ...Weather/Hazards Highlights... The primary focus for meaningful precipitation will likely continue to extend across the Alaska Peninsula, southern coast, and Panhandle at varying times. Western areas should have easterly low level flow already in place late this week and then flow ahead of any northward-moving Pacific waves just to the west may produce some moisture focus as well. There is now a less pronounced signal for some moisture to lift northward across the Panhandle around Friday, with precipitation trending lighter than in yesterday's guidance. Moisture from this and any trailing low-confidence waves could ultimately reach locations farther to the west. Shortwave energy initially crossing the mainland may produce light snow over parts of the western/northern mainland during the latter half of the week. Otherwise most of the mainland away from the southern coast should stay fairly dry. The deep storm affecting the Aleutians will initially bring a period of focused precipitation and strong winds with the leading front, followed by a rapid lighter/weaker trend. Confidence decreases for specifics of any additional waves that could focus precipitation and wind, though the general pattern should remain unsettled. The expected gradual weakening of upper ridging over the state after late this week should lead to a moderating trend for temperatures but with lows in particular still remaining above normal by the end of the period over most locations. Some pockets of below normal highs may develop over the interior. Rausch Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html